As a wireless LAN (local area network) and a wireless WAN (wide area network) have come into wide use, a large number of notebook computers (hereinafter, referred to as ‘notebook PCs’) recently sold have radio antennas for wireless communication built in as standard. The radio antennas are arranged at an upper side and a vertical side of a liquid crystal display such that the most satisfactory communication can be performed in a general position when a user operates the notebook PC. A plurality of antennas, for example, four or five antennas may be mounted in one notebook PC in order to meet a communication system in which a plurality of antennas are used, such as a diversity communication or an MIMO (multiple input multiple output) communication, or to meet a plurality of communication standards, such as a wireless LAN and a wireless WAN. Furthermore, in this specification, the housing which accommodates a liquid crystal display of a notebook PC therein is hereinafter referred to as a display-side housing, and a housing which accommodates therein main system elements constituting computers, such as a CPU, a mother board, and a hard disk, is hereinafter referred to as a main housing.
The electrical conductivity of a synthetic resin is very low. Accordingly, the wireless communication can be performed even if a radio antenna is covered with a housing formed of synthetic resin. In an early-stage notebook PC, a display-side housing was manufactured by using a rigid synthetic resin, and the radio antenna was attached to an inner wall of the housing. Then, in order to meet a request of a decrease in weight and thickness, the display-side housing came to be manufactured by using metal having high conductivity. For this reason, a structure in which a radio antenna is arranged at a portion where a part of a housing is cut out and a surface of the radio antenna is covered by a cap formed of a synthetic resin due to a request in terms of design and for safety has been adopted.
Known techniques regarding a structure in which a radio antenna is mounted in a display-side housing of a notebook PC are as follows. Japanese Unexamined Patent Publication No. 2002-149273, teaches a notebook PC which allows a radio antenna and a wireless module to be replaced when a part of a housing is detached. Japanese Unexamined Patent Publication No. 2003-202938, teaches a housing of a notebook PC in which a radio antenna is attached to an outer side surface of a display-side housing formed of metal and a side cover formed of a material having low conductivity is attached so as to cover the radio antenna. Japanese Unexamined Patent Publication No. 2004-280331, teaches a housing of a notebook PC in which a radio antenna is fixed in a shape protruding from a metal case, the periphery of the radio antenna is covered by a cover formed of a material having low conductivity, and a radio antenna portion is maintained in a shape spaced apart from an inner surface of the surrounding housing.
In a radio antenna, a gain or a resonance frequency changes due to an influence of a dielectric constant of a surrounding environment. Accordingly, a radio antenna used in the environment where a dielectric material is present in the neighborhood is manufactured in a condition, in which a distance up to the dielectric material when the radio antenna is used is set beforehand, such that a predetermined gain or resonance frequency can be obtained at the set distance. In this specification, a distance between a radiating element of a radio antenna and a dielectric material located near the radio antenna is hereinafter referred to as a set distance. When a display-side housing is manufactured using a synthetic resin which is a dielectric material, a radio antenna regularly functions even if the radio antenna is arranged inside a housing, but a predetermined gain may not be acquired or a resonance frequency may shift if a distance between the radio antenna and an inner wall of the housing deviates from the set distance. Accordingly, in the case that a surface of a radio antenna is covered by a dielectric material, it is necessary to maintain a set distance when the radio antenna is actually attached to a notebook PC.
In accordance with a known method of attaching a radio antenna to a display-side housing, a distance between an inner wall of the housing and a radio antenna is very short and is a fixed value. Therefore, the antenna characteristics intended when manufacturing the antenna can be obtained by setting the set distance to a distance between the radio antenna and the inner wall when the radio antenna is attached to the inner wall. Even in case where the display-side housing is manufactured using metal, the set distance can be realized when the radio antenna is actually attached to the notebook PC by causing a cap and the radio antenna to come in contact with each other.
In Japanese Patent Application No. 2007-69947, a new structure of a display-side housing, which is different from the known structure of the display-side housing formed of a rigid synthetic resin or metal, is proposed. In this structure, a function of the known display-side housing is divided into a strength function and a cover function, such that the strength function is assigned to an upper housing formed of metal and the cover function is assigned to a cosmetic cover formed of a synthetic resin. By adopting such a structure, a notebook PC may be further reduced in thickness and in weight. However, since a radio antenna needs to be arranged inside a cosmetic cover in terms of design, a study of attaching the radio antenna is required to secure the set distance.
For example, a method in which a radio antenna is attached to an inner wall of a cosmetic cover and then the cosmetic cover is attached to an upper housing may be considered. According to the method, a distance between the radio antenna and the cosmetic cover may be easily set to the set distance, but it takes time for wiring and connection of cables which run from the radio antenna attached to the cosmetic cover to a wireless module inside the housing. Although such housing structure is advantageous in that a user can detach a cosmetic cover in order to replace the cosmetic cover with one having a color or design that the user likes, the advantage might not be achieved if the radio antenna is attached to the cosmetic cover. In addition, it also takes time when disassembly and reassembly of the housing are performed as maintenance of a notebook PC.
As another method, a method in which a radio antenna is attached to an upper housing and a portion of a cosmetic cover corresponding to the radio antenna is cut out to secure transmission of an electric wave may be considered. In this case, since a problem related to safety or design remains if a radio antenna is exposed outside the housing, a cover is made using a cap formed of a dielectric material. For this reason, a study of maintaining a distance between a dielectric material and a radio antenna at a set distance is needed, and the strength of a cosmetic cover is decreased to deteriorate in terms of design.
Therefore a need has arisen to address the above-described shortcomings.